WO2006092910A1

WO2006092910A1 - Liquid containing dispersion stabilized catalytic nanoparticles

Info

Publication number: WO2006092910A1
Application number: PCT/JP2006/300193
Authority: WO
Inventors: Yuzuru Shimazaki; Yoshio Kobayashi; Mikio Konno
Original assignee: Tohoku Techno Arch Co., Ltd.
Priority date: 2005-02-28
Filing date: 2006-01-11
Publication date: 2006-09-08
Also published as: JP2006231266A; JP3870282B2

Abstract

This invention provides a colloidal solution characterized in that catalytic nanoparticles comprising (a) metal element-containing nanoparticles and (b) a layer of Pt or the like covering a part of the surface of the nanoparticle has been dispersion stabilized with a carboxylic acid compound such as citric acid. This colloidal solution can inhibit a reduction in active surface area caused by heat treatment of the catalyst in the use of metal nanoparticles having Pt or the like on the surface thereof as catalytic nanoparticles in a catalyst for a fuel cell electrode. There are also provided a catalyst for a fuel cell electrode prepared using the colloidal solution, and a fuel cell.

Description

Specification

Dispersed and stabilized liquid containing catalyst nanoparticles

Technical field

[0001] The present invention relates to a dispersion-stabilized catalyst nanoparticle-containing liquid and its application.

Background art

[0002] Fuel cells have the potential to achieve an energy density more than 10 times that of lithium-ion secondary batteries, and can be carried anywhere without charging if you carry the fuel. Expected to change. In particular, direct methanol fuel cells (DMFC) that use methanol as fuel are expected to be smaller and lighter and have lower costs. In addition, as a power source that can satisfy the demand for long-time driving for portable devices typified by mobile phones and laptop computers, it is compact but has excellent startability, load responsiveness, stability, and power generation as long as fuel is supplied. Attention is also drawn to the characteristics that it can be used for a long time.

Currently, in the development of fuel cells, particularly DMFC fuel cells, it is required to develop highly active materials as oxidation catalysts for electrodes.

Catalyst nanoparticles containing Pt are known to exhibit strong oxidation activity against hydrogen and alcohol, and are used as typical polymer electrolyte fuel cell (PEFC) electrode catalysts. However, since these catalysts that also have noble metal power are expensive, it is required to use them as little as possible. Therefore, it is necessary to make the catalyst more highly active in a small amount. When using the catalyst nanoparticles as an alcoholic acid catalyst, usually, the metal particles such as Ru coexist in the nanoparticles to poison the carbon monoxide produced as a reaction intermediate on the Pt surface. Suppress.

[0003] The PEFC electrode catalyst is prepared by reducing metal ions in the presence of carrier carbon in a solution and precipitating catalyst nanoparticles on the carrier carbon (deposition method: for example, Physica B 323 卷, p. 124 (2002) [Non-patent document 1]) and a method of adsorbing catalyst nanoparticles in a colloidal solution on a carrier carbon (colloid method: for example, Nano Letter 2 卷, 235 (2002) [Non-Patent Document 2]). According to colloid method, colloid solution Since the structure of the catalyst nanoparticles can be controlled during production, it is possible to produce a catalyst based on precise design. On the other hand, the dispersion stabilizer is usually adsorbed on the surface of the catalyst nanoparticles prepared by the colloid method, and it is necessary to heat-treat the prepared catalyst in order to expose the active surface.

[0004] The structure of Pt-Ru-based nanoparticles in catalysts prepared using colloidal methods has been

(1) Alloy nanoparticles of Pt and Ru (for example, Journal of Catalysts 195 卷, 383 Mitsugu (2000) [Non-patent Document 3]),

(2) Ru nanoparticles having Pt on the surface (for example, JP-A-2002-231257 [Patent Document 1]) have been reported. In particular, Ru nanoparticles having Pt on the surface have higher Pt utilization efficiency than Pt and Ru alloy nanoparticles because Pt having catalytic activity is concentrated on the particle surface. Since Pt is an expensive noble metal, the ability to reduce the amount of Pt in the catalyst is a great merit in terms of cost and environment.

[0005] Regarding the colloidal solution preparation technology of Ru nanoparticles having Pt on the surface, JP2002

-231257 [Patent Document 1] adsorbs hydrogen on the surface of Ru nanoparticles dispersed and stabilized with a polymer such as polybulurpyrrolidone to give reduction ability, and Pt ions on the surface of Ru nanoparticles. A technology for producing Ru nanoparticles with Pt on the surface by reduction is disclosed. However, in the catalyst prepared by the above technique, since the polymer covers the active surface, it is necessary to perform high temperature heat treatment at about 300 ° C. in the presence of hydrogen to decompose and remove the polymer. Therefore, there is a problem that the heat treatment induces aggregation of the catalyst nanoparticles and the active surface area decreases.

[0006] By the way, the reduction of Pt ions by citrate is described in, for example, Journal of Physical Chemistry 99, 14129 (1995) [Non-patent Document 4]. This paper describes that Pt nanoparticles can be prepared by thermal reduction of chloroplatinic (IV) acid with citrate. Further, the fact that kenic acid is adsorbed on the surface of the nanoparticles and stabilizes the nanoparticles is described in, for example, Science Engineering Symposium Series pages 56-35. However, there is no report on the reduction of Pt ions by citrate adsorbed on the nanoparticle surface.

Patent Document 1: Japanese Patent Application Laid-Open No. 2002-231257 Non-patent literature l: Physica B 323 卷, 124 (2002)

Non-Patent Document 2: Nano Letter 2 卷, 235 (2002)

Non-Patent Document 3 Journal of Catalysts 195 卷, 383 (2000)

Non-Patent Literature 4 Journal of Physical Chemistry 99, 14129 (1995) Disclosure of the Invention

Problems to be solved by the invention

[0008] In order to produce highly functional catalyst nanoparticles, it is necessary to stably hold the produced nanoparticles (dispersion stability) in a liquid medium as a production site. is there. That is, it is indispensable to disperse and stabilize the nanoparticles while avoiding aggregation. Therefore, when preparing colloidal solutions of metal nanoparticles having platinum group elements such as Pt on the surface, it has been essential to use polymers as dispersion stabilizers for nanoparticles. When a polymer is used for the catalyst, it is necessary to decompose and remove the polymer when preparing the catalyst even in the case of a colloid solution containing metal nanoparticles for the catalyst. Even if it is used, there has been a problem that, for example, a reduction in the active surface area is induced by heat treatment for polymer decomposition and removal. There is a need for the development of the handling and technology of the colloidal solution containing catalyst nanoparticles, which is inexpensive, simple and reliable.

Means for solving the problem

[0009] In order to overcome the above problems, the present invention, as a result of intensive research and investigation, (a) nanoparticles having a metal element, and (b) coating part or all of the surface of the nanoparticles It is found that the catalyst nanoparticles having a catalytically active metal layer such as a Pt layer are dispersed and stabilized in a colloidal solution by a carboxylic acid compound such as citrate, and further, a rubonic acid compound such as citrate. When the catalyst is prepared using a colloidal solution in which the catalyst nanoparticles are dispersed and stabilized, it is possible to avoid a decrease in the activity of the catalyst nanoparticles due to heat treatment, and the catalyst thus obtained is used as an electrode. As a result, the present inventors completed the present invention. Therefore, the present invention provides a catalyst nanoparticle force having (a) a nanoparticle having a metal element, and (b) a catalytically active element layer such as a Pt layer covering a part or all of the surface of the nanoparticle. Colloid by carboxylic acid compound such as acid A colloidal solution characterized by being dispersed and stabilized with a solution is provided. Also provided are a fuel cell electrode catalyst and a fuel cell produced using the colloid solution. By comparison, the present invention provides the following aspects.

[1] (a) nanoparticles having a metal element;

(b) a layer that covers a part or all of the surface of the nanoparticles and is made of a metal selected from platinum group metals;

A colloidal solution, characterized in that the catalyst nanoparticles are dispersed and stabilized with a strong rubonic acid compound in the colloidal solution.

[2] The colloid solution according to [1] above, which is a layer (b) force Pt layer according to [1].

[3] The metal element force described in (a) of [1] above, which is selected from the group consisting of Ru, Mo, W, Co, Fe and Ni Colloidal solution.

[4] The colloidal solution according to the above [1], wherein the metal elemental force Ru is as described in the above [1] (a).

[5] The colloidal solution as described in [1] above, wherein the carboxylic acid compound as described in [1] above is citrate.

[0010] [6] A nanoparticle-containing catalyst characterized in that catalyst nanoparticles are supported on a support using the colloidal solution according to any one of [1] to [5] above.

[7] The catalyst according to [6] above, which is a fuel cell electrode catalyst.

[8] A battery electrode characterized by using the catalyst according to [6] or [7]. [9] A fuel cell comprising the electrode according to [8].

[10] A fuel cell electrode characterized in that a catalyst produced using the colloidal solution according to any one of [1] to [5] is used as an electrode catalyst.

[11] A fuel cell characterized in that a catalyst produced using the colloidal solution according to any one of [1] to [5] is used as an electrode catalyst.

[12] A metal salt-containing liquid containing a carboxylic acid compound as a dispersion stabilizer is subjected to colloid formation conditions to form nanoparticles having metal elements, and then a platinum group metal salt-containing liquid is added. Reduction treatment, containing catalyst nanoparticles, and the catalyst nanoparticles are Colloidal solution dispersed and stabilized by acid compound

Here, the catalyst nanoparticles are

(a) a nanoparticle having a metal element;

Have

A process for producing a colloidal solution, characterized in that

[13] The colloidal solution according to any one of the above [1] to [5] is mixed with a catalyst carrier, and catalyst nanoparticles are supported on the carrier to obtain a nanoparticle-containing catalyst. Yes Catalyst manufacturing method.

[14] The method for producing a catalyst according to [13], wherein the catalyst is produced by high-temperature heat treatment according to the method for producing a catalyst according to [13].

[15] The method for producing a catalyst as described in [13] above, wherein the high-temperature heat treatment is performed at about 250 ° C or higher, but the heat treatment is not applied.

The invention's effect

The carboxylic acid compound such as citrate adsorbed on the surface of the catalyst nanoparticle contained in the fuel cell electrode catalyst of the present invention has a weak adsorption force on the surface of the catalyst nanoparticle. When used as a catalyst, the surface force of the catalyst nanoparticles is desorbed. Therefore, a heat treatment for cleaning the catalyst nanoparticle surface does not induce a reduction in the active surface area, and a catalyst having a clean and highly functional catalyst nanoparticle surface can be obtained. It is out.

Other objects, features, excellence and aspects of the present invention will be apparent to those skilled in the art from the following description. However, the description of the present specification, including the following description and the description of specific examples, etc., shows preferred embodiments of the present invention and is shown only for explanation. It was understood that! Various changes and Z or alterations (or modifications) within the spirit and scope of the present invention disclosed herein will occur to those skilled in the art based on the following description and knowledge from other parts of the present specification. Will be readily apparent. All patent documents and references cited in this specification are intended to be illustrative. Which are intended to be incorporated herein by reference as part of the specification.

Brief Description of Drawings

FIG. 1 is a schematic diagram of catalyst A (Example 1).

FIG. 2 is a schematic diagram of Catalyst B (Comparative Example 1).

Explanation of symbols

[0014] 1 Ru nanoparticles

2 Chenic acid molecule

3 Pt layer

4 Carrier carbon

11 Pt layer

12 Polybylpyrrolidone molecule

13 Ru nanoparticles

14 Carrier carbon

BEST MODE FOR CARRYING OUT THE INVENTION

[0015] The colloidal solution of the present invention is obtained by subjecting the coexisting platinum group transition metal ions to reducing conditions in a colloidal solution of metal nanoparticles stabilized with a carboxylic acid compound, thereby reducing the metal nanoparticle. Force that can be prepared by supporting the platinum group transition metal on part or all of the surface of the particle The carboxylic acid compound adsorbs on the surface of the metal nanoparticle and It contributes to stable dispersion, stabilizes the colloidal solution, and also has a suitable effect on the reduction reaction, and is useful for forming a platinum group metal layer on part or all of the surface of the nanoparticle. is there. Particularly preferably, the colloidal solution of the present invention is used in the colloidal solution of metal nanoparticles stabilized with taenic acid, and uses the reducing ability of citrate adsorbed on the surface of the metal nanoparticles. It is prepared by reducing Pt ions and supporting the generated Pt layer on part or all of the surface of the metal nanoparticles. Examples of the platinum group transition metal include those in which Pt, Ru, Ir, Pd, Os, and Rh force are also selected, and may be one of them or a mixture thereof. Pt is preferable. Examples of the carboxylic acid compound include monocarboxylic acid, dicarboxylic acid, tricarboxylic acid, and tetracarboxylic acid. Also included are those having functional groups such as hydroxyl groups and keto groups, and those having 1 to 12 carbon atoms, and further containing carbon chains may be linear or branched There may be. Typical examples include hydroxycarboxylic acid compounds, and for example, citrate is preferred.

[0016] The metal nanoparticles are composed of metal elements Ru, Mo, W, Co, Fe, and Ni that have an effect of suppressing adsorption of carbon monoxide on the surface of the platinum group transition metal layer (for example, the surface of the Pt layer). It is preferable that one or more kinds of poisoning suppression elemental powers selected are configured (however, elements different from those constituting the platinum group transition metal layer are usually selected). The metal nanoparticles can be obtained by subjecting a solution (for example, an aqueous solution) containing a metal salt to colloid formation conditions to precipitate the metal colloid. Typically, metal nanoparticles can be formed by a method such as stirring an aqueous solution of the above metal salt in the presence of a reducing reagent. In addition, the particle diameter of the metal nanoparticles is preferably in the range of lnm to 10 nm, which varies depending on the size of the platinum group transition metal layer (for example, Pt layer) that is reduced and supported on the surface. If it is less than 1 nm, it is not preferable because a sufficient poisoning suppression effect cannot be given to the surface of the supported platinum group transition metal layer (for example, Pt layer). On the other hand, the thickness of 10 nm or more is not preferable because the number of metal atom portions not involved in the suppression of poisoning on the surface of the platinum group transition metal layer (for example, Pt layer) increases and the cost increases. The particle size can be evaluated by an electron microscope or X-ray diffraction measurement.

The colloidal solution of the metal nanoparticles can be prepared by reducing the metal ion in a solution having a carboxylic acid compound and a metal ion. The reduction of the metal ion can be usually performed by adding a reducing agent to the solution while stirring the solution. The colloid formation condition may be that metal ions are gradually reduced by agitating the metal salt-containing liquid under reducing conditions to form fine particles having metallic strength. The reducing conditions may be, for example, maintaining a solvent in a hydrogen atmosphere and achieving a condition in which the hydrogen atmosphere is in contact with the solution, or adding a reducing reagent to the solution. As the reducing reagent, one selected from those known to those skilled in the art can be used. 1S For example, sodium borohydride, sodium trimethoxyborohydride, sodium borohydride, triacetoxyborohydride Sodium, tri-s-butylborohydride Lithium lithium, potassium tri-s-butylborohydride, lithium triciamylborohydride, potassium triciamylborohydride, lithium hydrogenated trialkoxyboron, potassium trialkoxyborohydride, lithium triethylborohydride, lithium borohydride Zinc, sodium borohydride such as calcium borohydride or lithium borohydride and related compounds, lithium aluminum hydride, trialkoxy derivatives LiAlH (0 R) and bis (2-methoxyethoxy) alum hydride Metal hydrogen complex such as sodium sodium

Three

, Borane, diborane, complexes of borane with THF, dimethylsulfide, amines, etc., texylborane, disiamilborane, 9-borabicyclo [3.3.1] nonane, catecholborane, isopinocamphanylborane, etc. alkylborane, hydrazine Thioethanolamine, dithiothreitol, reduced dartathione, cysteine and the like.

[0018] In a preferred embodiment of the present invention, the colloidal solution of the metal nanoparticles is preferably prepared by reducing the metal ion in a solution containing citrate and metal ions. The metal ions are preferably reduced by adding a reducing agent to the solution while stirring the solution. The reducing agent is not particularly limited as long as it is a reagent that reduces the metal ion, and examples thereof include hydrogen, sodium borohydride, dimethylamine borane, hydrazine, and hydroxylamine. The solvent applied to the colloidal solution varies depending on the solubility of the metal salt. Water, alcohols such as methanol and ethanol, ketones such as acetone and methyl ethyl ketone, esters such as ethyl acetate, acetonitrile, Highly polar solvents such as dimethylformamide, dimethyl sulfoxide, sulfolane and diglyme are preferred. In particular, hydrophilic organic solvents such as water or alcohol mixed with water and ketones can be suitably used. In addition, the concentration of the metal ion is preferably in the range of 0.001% to 0.1% force that varies depending on the solvent in which the metal salt is dissolved. If it is less than 0.001%, the amount of metal nanoparticles formed is not sufficient, and if it exceeds 0.1%, aggregates of metal nanoparticles are not preferable. On the other hand, the concentration of citrate is preferably 0.001%, which varies depending on the solvent, and a saturated concentration of taenoic acid. If it is less than 0.001%, the metal nanoparticles are not sufficiently dispersed and stabilized, and an aggregate is formed. In addition, when the concentration is higher than the saturated concentration of citrate, it is not preferable because of precipitation of citrate.

[0019] By comparison, typical methods for producing the colloidal solution include: (1) Carboxylic acid compounds (for example, A metal salt-containing liquid (for example, a Ru ion-containing liquid) containing quanic acid as a dispersion stabilizer is subjected to colloid formation conditions to form nanoparticles having a metal element (for example, Ru nanoparticles). (2) A platinum group metal salt-containing liquid (for example, a Pt ion-containing liquid) is added to the catalyst, followed by reduction treatment, containing catalyst nanoparticles, and the catalyst nanoparticles are a carboxylic acid compound (for example, quenate). (Wherein the catalyst nanoparticles cover a part or all of the surface of the nanoparticles with (a) nanoparticles containing metal elements (eg Ru nanoparticles) and (b) And a layer made of a metal selected from a platinum group metal (for example, a Pt layer).

[0020] Platinum salts include those comprising Pt ²⁺ , Pt ³⁺ , or Pt ⁴⁺ , and PtX

2

, PtX, PtX, [PtA] X, M ¹ [PtX], M ¹ [PtX Y], M ^ PtX Y], M ^ PtX Y], M ¹ [PtX] (X

3 4 6 2 2 4 2 2 2 3 2 2 2 6 and Y are all F-, Cl-, Br-, Γ, OH-, CN-, NO-, N-, CH COO ", SCN-, Asechi

3 3 3

Anions such as lucacetonate, 1 / 2SO ² , 1 / 2CO ² —, etc. M ¹ is K, Na or Η

4 3

It is a monovalent cation, and A is NH or amines).

Three

Specifically, PtCl, PtBr, Ptl, Pt (CN), Pt (SCN), PtCl, PtBr, Ptl, PtF, PtCl,

2 2 2 2 2 3 3 3 4 4

PtBr, Ptl, K [PtCl (acac)], H PtCl and the like.

4 4 2 2 2 2 6

Ruthenium salts include R _u ²⁺ , Ru ³⁺ or Ru ⁴⁺ , RuX, RuX, RuX,

2 3 4

[RuX] M ^] , M ^] [RuX] (X is a halogen such as Cl and Br, anions such as NO- and SO, M ¹

6 3 4 3 4

Is a monovalent cation such as K, Na, Rb, Cs or H). Specifically, RuCl, ((NH) RuCl, Ru (SO;), RuS, RuO, RuO, Na RuO, K Ru

3 4 2 6 4 2 2 2 4 2 4 2

O etc. are illustrated.

Four

[0021] The iridium salt, Ir +, Ir ^2+, those comprising Ir ³⁺ or ^{Ir 4+, IrX, IrX, IrX} , IrX

2 3 4

, [IrX JM ¹ , M ^J [IrX] (X is a halogen such as Cl and Br, anion such as SO, M ¹ is K,

6 3 4 4

It is a monovalent cation such as Na, Rb, Cs or H. ) And the like. Specifically, KIr (SO 2), RbIr (SO 2), CsIr (SO 2) and the like are exemplified.

4 2 4 2 4 2

Palladium salts contain Pd ²⁺ and can usually be represented in the form of Pd-Z

2

. Z is a salt of halogen such as Cl, Br, and I, acetate, trifluoroacetate, acetylacetonate, carbonate, park mouthrate, nitrate, sulfate, oxide, and the like. Specifically, PdCl, PdBr, Pdl, Pd (OCOCH), Pd (OCOCF), PdSO, Pd (N O), PdO and the like.

3 2

[0022] As the osmium salt, Os +, Os ^2+, those comprising Os ³⁺ or Os ^4+, OsX, OsX, O

2 sX, OsX, [OsX] M ^] , M '[OsX] (X is a halogen such as Cl or Br, anion such as SO

3 4 6 3 4 4

M ¹ is a monovalent cation such as K, Na, Rb, Cs or H). Specifically, OsBr, OsO, OsCl, KOs (SO), RbOs (SO), CsOs (SO), etc.

4 4 4 4 2 4 2 4 2 Illustrated.

Rhodium salts include Rh ³⁺ , RhX, Rh X, [RhA] X, M ¹ [RhX], M

3 2 6 6 3 3 6

'[RhX] (X is a halogen such as F or CI, anion such as CN or SO, M ¹ is K or Na

4 4

Is a monovalent cation such as H, and A is NH or an amine. ) Etc.

Three

it can. Specifically, Rh 0, RhO, Rh (SO), Rh (OH), Rh (NO), RhCl, RhF, Rh

2 3 2 2 4 3 3 3 3 3 3

CN, KRh (SO), Na RhCl, NaRh (SO), HRh (SO) and the like are exemplified.

3 4 2 2 4 4 2 4 2

Metal salts such as Mo, W, Co, Fe, and Ni can also be appropriately selected from those known in the field or the field of inorganic chemistry, and water-soluble salts are preferably used. It is not limited to it. Examples of the salts include those containing halogens such as Cl, Br, and I, organic acid salts such as sulfates, nitrates, halogen peroxides, and acetates, and various double salts.

[0023] Further, the coating ratio of the Pt layer supported on the surface of the metal nanoparticles is not particularly limited as long as the Pt surface area necessary for obtaining the required catalytic activity can be ensured. It is desirable to be 5% or more of the surface area of the genus nanoparticles. The thickness of the Pt layer is not limited as long as the metal nanoparticles affect the electronic state of the Pt atoms existing on the surface of the Pt layer, but the thickness of the lPt atomic layer is in the range of 3 nm. Is preferred. If it is 3 nm or more, the metal nanoparticles do not affect the electronic state of the Pt atoms present on the surface of the Pt layer, and the effect of inhibiting the oxidation of carbon and carbon on the surface of Pt cannot be obtained. The particle diameter can be evaluated by an electron microscope or X-ray diffraction measurement.

[0024] The catalyst of the present invention, particularly the catalyst for a fuel cell electrode, can be obtained by supporting the catalyst nanoparticles on a support using the catalyst nanoparticle-containing colloidal solution. In a typical method, the colloidal solution is mixed with a catalyst support, and catalyst nanoparticles are supported on the support to obtain a nanoparticle-containing catalyst. In the production method of the catalyst, What has the characteristic that heat processing is not given is preferable. The high-temperature heat treatment refers to a material that is applied at about 250 ° C or higher, for example, including exposure to a high temperature of 300 ° C, or even in a hydrogen atmosphere. It may mean that the heat treatment is carried out under the reducing conditions and the step of decomposing Z or polymer.

[0025] In a typical case, the fuel cell electrode catalyst of the present invention is composed of the catalyst nanoparticles and a carrier strength of one bon. The carrier carbon is not particularly limited as long as it is conductive carbon, but preferably has a high surface area because it is necessary to adsorb a large amount of the catalyst nanoparticles. As a force bon used to constitute the electrode, powdery, fibrous, granular, etc. can be used according to the purpose as appropriate, and a mixture thereof can also be used. Typical force-bons include force-bon powder, spherical force-bon black, scaly graphite, pitch, fibrous carbon, and hollow carbon balloon. A variety of carbon blacks are known and can be characterized by particle size, specific surface area, nitrogen pore volume, oil absorption, etc. Examples include VULCAN ™ XC72R (Cabot), BLACK PEAR LS ™ 2000 (Manufactured by Cabot), ketjen black, furnace black, acetylene black, activated charcoal and the like. Examples of the fibrous carbon include isotropic pitch-type, liquid crystal pitch-type, and PNA-type, and a commercially available medium force can be selected and used. In addition, the fuel electrode catalyst of the present invention can obtain the desired effect of the present invention without being subjected to heat treatment, but in order to remove impurities on the surface of the catalyst nanoparticles, heat treatment is performed as necessary. It is also possible. At this time, kenic acid undergoes thermal decomposition at a lower temperature than the polymer, and therefore, heat treatment at a lower temperature is required than when the polymer is used as a dispersion stabilizer. Therefore, the reduction of the active surface area of the catalyst by heat treatment is less than when using a polymer.

[0026] The catalyst obtained in the present invention is perfluorosulfonic acid (Perfluorosulfonic acid) according to a conventional method.

Acid) / PTFE copolymer (H ") type and other polymer electrolyte membranes such as perfluorocarbon membranes can be blended with a substrate and then applied to carbon paper to form an electrode. The electrolyte membrane can be selected from those known to those skilled in the art in the art. For example, Nafion ™ is a registered trademark of DuPont) What is sold with the brand name of can be used conveniently. The molded body obtained by force can be suitably used as an electrode of a PEFC fuel cell, for example, an anode. In particular, it can be installed in methanol fuel cells (DMFC) for next-generation mono-electronic devices. A new high-performance fuel cell can be constructed by replacing the existing anode of a fuel cell known in the art with the electrode of the present invention. Therefore, even batteries having a structure known in the art include all batteries using the catalyst of the present invention.

[0027] Hereinafter, the present invention will be specifically described with reference to examples and comparative examples. However, these examples are provided merely for the purpose of describing the present invention and for reference to specific embodiments thereof. It is. These exemplifications are for explaining specific specific embodiments of the present invention, and are not intended to limit or limit the scope of the invention disclosed in the present application. In the present invention, it should be understood that various embodiments based on the idea of the present specification are possible. All examples were performed or can be performed using standard techniques, except as otherwise described in detail, and are well known to those skilled in the art and are It is.

Example 1

[0028] Fig. 1 is a schematic view of a catalyst prepared by using a citrate-stable catalyst nanoparticle colloidal solution in which a Pt layer is supported on the surface of Ru nanoparticles. The catalyst shown in Fig. 1 (Catalyst A) was prepared by the following method.

First, an aqueous solution (496 mL) containing 38 mg of citrate (manufactured by Wako Pure Chemical Industries), 40 mg of ruthenium (III) chloride n-hydrate (manufactured by Wako Pure Chemical Industries), 40 mg of sodium hydroxide (manufactured by Wako Pure Chemical Industries) An aqueous solution (4 mL) in which 38 mg of sodium borohydride (manufactured by Wako Pure Chemical Industries) was dissolved was added, and stirred for 1 day to prepare a Ru nanoparticle colloid solution stabilized with taenic acid. Thereafter, an aqueous solution (2.5 mL) containing 47 mg of platinum chloride (IV) acid hexahydrate (manufactured by Wako Pure Chemical Industries, Ltd.) was added, and nitrogen publishing was performed. Thereafter, the colloidal solution was refluxed at the boiling point of the colloidal solution for 5 hours to obtain a colloidal solution of Ru nanoparticles carrying a Pt layer.

[0029] In this colloidal solution, 27 mg of an aqueous dispersion (10 mL) of BLACK PEARL 2000 (manufactured by Cabot) was added and irradiated with ultrasonic waves for 5 hours, followed by centrifugal separation Z drying to obtain catalyst A. Catalyst A permeation type Observation with an electron microscope confirmed that a Pt layer was supported on Ru nanoparticles. The size of the Ru nanoparticles was about 5 nm, and the thickness of the Pt layer was about 2 nm. Further, the weight fraction of Ru in the catalyst A was 15 wt%, and the weight fraction of Pt was 31 wt%.

[0030] Next, 50 mg of Catalyst A and 600 mg of 5% Nafion ™ 117 solution (manufactured by Wako Pure Chemical Industries, Ltd.) were mixed to prepare a slurry. Thereafter, the slurry was applied to carbon paper (TGP-H-060: manufactured by Toray) so that the dry weight of the mixture of catalyst A and Nafion ™ 117 was 16 mg, thereby producing an electrode. The surface area of the electrode was 3 cm ² . Evaluation of methanol oxidation current of this electrode

A current value of 108 mA was obtained at 0.7 V (vs. NHE).

[0031] Therefore, the catalyst nanoparticles having a clean surface that does not undergo a heat treatment that induces a reduction in the active surface area due to the desorption effect of the catalyst surface force of citrate, and that supports the Pt layer on the surface of the Ru nanoparticles. The catalyst which has was able to be obtained.

(Comparative Example 1)

FIG. 2 is a schematic diagram of a catalyst prepared using a polymer-stable catalyst nanoparticle colloidal solution in which a Pt layer is supported on the Ru nanoparticle surface. It can be seen that the surface of the catalyst (catalyst nanoparticle surface) is covered extensively with the polymer, preventing the expression of activity. The catalyst shown in FIG. 2 (Catalyst B) was prepared by the following method.

Ethanol-water mixed solution (496 mL) in which 38 mg of polymer polybutyrrolidone (PVP: Wako Pure Chemical Industries, Ltd.) and 24 mg of ruthenium (III) chloride n hydrate (Wako Pure Chemical Industries, Ltd.) are dissolved An aqueous solution (4 mL) in which 38 mg of sodium borohydride (manufactured by Wako Pure Chemical Industries) was dissolved was added to the solution and stirred for 1 day to prepare a Ru colloid solution stabilized with PVP. The colloidal Ru particles separated by ultrafiltration were washed and dispersed in an equal volume mixture of water-ethylene glycol-ethanol. Hydrogen was published in this Ru colloid solution to adsorb hydrogen to Ru colloidal particles, and then degassed with nitrogen. A solution containing 47 mg of platinum (IV) chloride hexahydrate (manufactured by Wako Pure Chemical Industries, Ltd.) (2.5 mL) ) Was added dropwise to prepare a PVP-stabilized catalyst nanoparticle colloidal solution carrying a Pt layer on the surface of Ru nanoparticles.

In this colloidal solution, 27 mg of an aqueous dispersion (10 mL) of BLACK PEARL 2000 (manufactured by Cabot) was added and subjected to ultrasonic irradiation for 5 hours, followed by centrifugal separation Z drying to obtain catalyst B. Catalyst B was observed with a transmission electron microscope, and it was confirmed that a Pt layer was supported on Ru nanoparticles. Ru nano The particle size was about 5 nm, and the thickness of the Pt layer was about 2 nm. The weight fraction of Ru in catalyst B was 24 wt%, and the weight fraction of Pt was 20 wt%.

[0034] Next, 50 mg of Catalyst B and 600 mg of 5% Nafion ™ 117 solution (manufactured by Wako Pure Chemical Industries, Ltd.) were mixed to prepare a slurry. Thereafter, the slurry was applied to carbon paper (TGP-H-060: manufactured by Toray) so that the dry weight of the mixture of catalyst B and Nafion ™ 117 was 16 mg, and an electrode was produced. The surface area of the electrode was 3 cm ² . When the methanol oxidation current of this electrode was evaluated, almost no current was observed at any potential (less than 10 mA at 0.7 V (vs. NHE)).

Industrial applicability

[0035] According to the present invention, it is possible to provide a highly functional catalyst composed of nanoparticles that maintain high activity, so that an inexpensive fuel cell electrode and the like can be obtained despite its excellent function. Can be provided. By using the highly active and highly functional nanoparticle catalyst, the problem of instability such as agglomeration unique to nanoparticles can be solved, while the nanoparticles can be used while maintaining high activity. The field of application can be expanded. In particular, it is possible to provide an inexpensive and stable high-capacity battery in the field of portable power sources and the like. It is clear that the present invention can be carried out in addition to those described in the above description and examples. . Many modifications and variations of the present invention are possible in light of the above teachings, and thus are within the scope of the claims appended hereto.

Claims

The scope of the claims

[1] (a) nanoparticles having a metal element;

[2] The colloidal solution according to claim 1, which is a layer (b) force Pt layer according to claim 1.

[3] The colloid according to claim 1, wherein the metal elemental force according to claim 1 (a) is selected from a group force consisting of Ru, Mo, W, Co, Fe and Ni. solution.

[4] The colloidal solution according to claim 1, wherein the metal element according to (a) of claim 1 is Ru.

[5] The colloidal solution according to [1], wherein the carboxylic acid compound according to [1] is citrate.

[6] A nanoparticle-containing catalyst, wherein the catalyst nanoparticle is supported on a support using the colloidal solution according to any one of claims 1 to 5.

[7] A battery electrode comprising the catalyst according to claim 6.

[8] A fuel cell comprising the electrode according to claim 7.

[9] A metal salt-containing liquid containing a carboxylic acid compound as a dispersion stabilizer is subjected to colloid formation conditions to form nanoparticles having metal elements, and then a platinum group metal salt-containing liquid is added, A colloidal solution containing catalyst nanoparticles that has been subjected to reduction treatment, and wherein the catalyst nanoparticles are dispersed and stabilized by a carboxylic acid compound

Here, the catalyst nanoparticles are

(a) a nanoparticle having a metal element;

(b) covering part or all of the surface of the nanoparticles;

A layer of a metal selected from platinum group metals;

Have

A process for producing a colloidal solution, characterized in that A method for producing a catalyst, characterized in that the colloidal solution according to any one of claims 1 to 5 is mixed with a catalyst support, and catalyst nanoparticles are supported on the support to obtain a nanoparticle-containing catalyst. .